A wavelength conversion technique to obtain, for example, green fluorescent light or red fluorescent light by irradiating a phosphor with excitation light having short wavelength (e.g., excitation light emitted from the blue laser) and to utilize the obtained fluorescent light as illumination light has been known. A solid light source such as the blue laser represents a light source device having a good responsiveness. Hence, solid light sources are widely utilized in an image projection apparatus (hereinafter, simply referred to as a projector). The projector then obtains several types of illumination light (e.g., green illumination light) efficiently in accordance with the wavelength conversion technique.
The projector can obtain the illumination light and guide the illumination light onto a display panel of the projector more efficiently when the light source is smaller. Accordingly, most of projectors condense the excitation light before irradiating the phosphor with the excitation light. However, these projectors may not have enough irradiation area to irradiate the phosphor with the excitation light, and, therefore, cannot obtain enough fluorescent light intensity. To overcome such a deficiency, a projector that installs a phosphor on a light guide member, which guides illumination light, has been developed (see Patent Literatures 1 and 2).
Patent Literature 1 discloses a projector that includes a translucent rod (light guide member) containing a phosphor as a light tunnel, allows the excitation light to enter the light tunnel, and outputs fluorescent light generated in the light tunnel in accordance with light-guiding action of the light tunnel.
In the technique of Patent Literature 1, the fluorescent light generated by the phosphor passes through the translucent rod where the phosphor itself is included. However, this decreases the transmittance of the translucent rod and loses the light guided to the emission port. That is, it is difficult to obtain high efficient fluorescent light.
Patent Literature 2 discloses a projector that includes a plurality of optical paths for excitation light, and sequentially irradiates a plurality of phosphors coating the inside of a light tunnel with the excitation light beam so as to obtain fluorescent light having a required wavelength. The fluorescent light generated by the phosphors is repeatedly reflected inside the light tunnel such that the illumination distribution is equalized before the fluorescent light is emitted from an emission port. Therefore, it is possible to guide the fluorescent light to the emission port as illumination light. Similar to the technique of Patent Literature 2, a technique to obtain illumination light efficiently should be developed.